PROSPECTIVE parents are waiting more than four and a half years for the completion of overseas adoptions, official figures show.

The Australian Institute of Health and Welfare (AIHW) says it took an average of 56 months for the processing of an inter-country adoption in 2011-12, compared to 37 months in 2007-08.

AIHW spokesman Tim Beard said the dramatic increase could be attributed to lengthening processing times in other countries - which are now an average of 30 months, up from 19 months four years ago.

"Processing times are affected by factors such as the number and characteristics of children in need of adoption, the number of applications received and the resources of the overseas authority," he said.

"These are all factors outside the control of Australian authorities."

Despite the lengthy waits, Mr Beard said Australian adoption authorities had actually improved their own processing times.

The total number of completed adoptions in Australia in 2011-12 was just 333 - a record low and a steep decline from the 384 finalised in the previous year, the figures show.

The number was 1494 in 1987-88.

Among the adoptions finalised in 2011-12, overseas children outnumbered Australian children for the first time.

Mr Beard said the generational decline in adoptions reflected social and legislative changes.

A NOTE ABOUT RELEVANT ADVERTISING: We collect information about the content (including ads) you use across this site and use it to make both advertising and content more relevant to you on our network and other sites.